Inclusion Criteria:

Subjects eligible for inclusion in this study must fulfill all the following criteria:

• Subjects must be able to understand and comply with the requirements of the study and communicate with the investigator. Subjects must give written, signed, and dated informed consent before any study related activity is performed. When appropriate, a legal representative will sign the informed consent according to local laws and regulation.
• Both men and women must be at least 18 years of age at the time of screening.
• Subjects must have clinical and histological features of LP.
• LP up to 20% of the BSA.
• Subjects must have a minimum of 4 lesions; ideally, 10 lesions of LP.
• Subjects must have treatment naïve cutaneous LP or treatment refractory disease, as defined by failure of at least one established treatment for LP:
  • Failure of prior therapy:
    • Topical treatment;
    • Systemic immunosuppressant;
    • Oral metronidazole;
    • Oral sulfasalazine;
    • Oral retinoid.

Exclusion Criteria:

Subjects fulfilling any of the following criteria are not eligible for inclusion in this study. To ensure the recruitment of a representative sample of all eligible subjects, the investigator may apply no additional exclusions.

• On excluded therapies, not on a stable dose of a therapy, or incompletely washed out for a therapy.
• Known hypersensitivity to any component of INCB018424 PHOSPHATE CREAM.
• Variants of LP deemed by the investigators to be inappropriate for INCB018424 PHOSPHATE CREAM including by not limited to:
  • Erosive LP;
  • Intertriginous LP;
  • Oral LP;
  • Facial LP;
  • Drug-induced LP;
  • Vaginal LP.
• LP involving greater than 20% BSA.
• Pregnant or nursing (lactating) women (pregnancy is defined as the state of a female after conception and until the termination of gestation, confirmed by a positive human chorionic gonadotropin (hCG) laboratory test).
• Women of childbearing potential [Post-menopausal or not of child-bearing potential is defined by: 1 year of natural (spontaneous) amenorrhea or Surgical bilateral oophorectomy (with or without hysterectomy), total hysterectomy or tubal ligation at least 6 weeks ago. Oophorectomy alone must be confirmed by follow up hormone level assessment to be considered not of child-bearing potential, defined as all women physiologically capable of becoming pregnant, unless they are using basic methods of contraception which includes:
  • Total abstinence (Periodic abstinence and withdrawal are not acceptable methods of contraception);
  • Female sterilization (bilateral oophorectomy with or without hysterectomy), total hysterectomy, or tubal ligation at least 6 weeks before taking study treatment. Oophorectomy alone requires follow up hormone level assessment for fertility;
  • Male sterilization (at least 6 months prior to screening). The vasectomized male partner should be the sole partner for that subject;
  • Barrier methods of contraception: condom or occlusive cap;
  • Use of oral, injected or implanted hormonal methods of contraception or other forms or hormonal contraception that have complete efficacy (failure <1%). (The dose of the contraceptive should be stable for 3 months).
• Active ongoing inflammatory diseases of the skin other than LP that might confound the evaluation of the benefit of INCB018424 PHOSPHATE CREAM.
• Underlying condition (including, but not limited to metabolic, hematologic, renal, hepatic, pulmonary, neurologic, endocrine, cardiac, infectious or gastrointestinal conditions) which, in the opinion of the investigator, significantly immunocompromised the subject and/or places the subject at unacceptable risk for receiving an immunomodulatory therapy.
• Active systemic infections during the 2 weeks prior to randomization (common cold viruses not included) or any infection that reoccurs on a regular basis.